[@types/moment-timezone] Fix return type of tz function in Moment interface (#28453)

Unless moment.Moment is specified, IDEs think the function's return type is the Moment interface that contains the function.

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types/moment-timezone/index.d.ts

@@ -58,7 +58,7 @@ declare module "moment" {
 
     interface Moment {
         tz(): string | undefined;
-        tz(timezone: string, keepLocalTime?: boolean): Moment;
+        tz(timezone: string, keepLocalTime?: boolean): moment.Moment;
         zoneAbbr(): string;
         zoneName(): string;
     }